Filter assembly

ABSTRACT

The invention provides a filter assembly for use in a vacuum cleaner having a first filter portion that includes a foam filter, and a second filter portion located downstream of the first filter portion and containing a HEPA grade filter medium, the first and second filter portions being held directly adjacent one another. The first filter portion also includes an electrostatic filter located on a side of the foam filter facing the second filter portion. The foam filter of the first filter portion is, in use, exposed directly to a dust-laden airflow. The provision of the electrostatic filter on the foam filter eliminates the possibility of dust initially retained by but later released from the foam filter escaping from the first filter portion.

The invention relates to a filter assembly. Particularly, but notexclusively, the invention relates to a filter assembly designed andadapted for use in a vacuum cleaner. More particularly, the inventionrelates to a filter assembly for use in a vacuum cleaner and which isused to protect the motor and fan unit.

Motor filter assemblies for removing dust remaining entrained in the airstream of a vacuum cleaner or other dust retaining appliances arecommon. Such filter assemblies generally comprise at least one filterlocated in a filter housing. Commonly, two or three filters are arrangedin series in the filter assembly to maximise the amount of dust capturedby the filter assembly. A known type of filter comprises a first foamfilter which is located directly in the air stream and has a large dustretaining capacity. An electrostatic or HEPA grade filter, which iscapable of trapping very small dust particles, in particular particlesof less than one micron, is then provided downstream of the foam filterto retain any dust which escapes from the foam filter. In such a knownarrangement, little or no dust is able to exit the filter assembly. Itis known to provide a foam filter which is removable from the filterassembly for cleaning. WO 99/12635 discloses an air filter forrespiratory apparatus comprising a series of filters; foam,electrostatic and HEPA. The filters are located in two separatehousings, a first housing having a washable foam pre-filter and a secondhousing having both electrostatic and HEPA grade filters. The foampre-filter retains the major portion of the entrained dust and isremovable for cleaning. However, this arrangement is limited in that theelectrostatic or HEPA grade filters, which retain dust which may escapethe foam pre-filter, cannot be removed for cleaning. Therefore, thefilters in the second housing will require to be replaced at frequentintervals.

It is an object of the present invention to provide a filter assemblysuitable for use in a vacuum cleaner or other appliance which has alarge capacity for retaining dust and wherein the filter components ofthe filter assembly do not require to be replaced at frequent intervals.It is a further object of the present invention to provide a filterassembly which retains the ability to contain dust under large backpressures. Further, it is an object of the present invention to providea filter assembly for use in a vacuum cleaner or other appliance inwhich the motor is reliably protected and in which the maintenance costsof the vacuum cleaner or other appliance are reduced.

The invention provides a filter assembly for use in a vacuum cleanerhaving a first filter portion comprising a foam filter, and a secondfilter portion located downstream of the first filter portion andconsisting of a HEPA grade filter medium, the first and second filterportions being held directly adjacent one another by means of a filterhousing, the foam filter of the first filter portion being, in use,exposed directly to a dust-laden airflow, and the first filter portionbeing removable from the filter assembly, characterised in that thefirst filter portion further comprises an electrostatic filter locatedon the side of the foam filter facing the second filter portion. In suchan arrangement, any dust which may escape from the foam filter istrapped by the electrostatic filter before it reaches the HEPA filter.Little or no dust will be deposited on the HEPA filter under normal useconditions. This prolongs the life of the HEPA filter since it iseffective to separate dirt and dust only under extreme conditions, whichare infrequent. Further, the foam filter and the electrostatic filtercan be removed for cleaning in a single operation.

Preferably, the electrostatic filter is bonded to the foam filter.Bonding the electrostatic filter to the foam filter ensures that therecan be no misplacement or misalignment of the electrostatic filter. Ifthe electrostatic filter were inaccurately positioned, dust that mightotherwise have been trapped in the electrostatic filter will pass to theHEPA filter. If this were to happen, the HEPA filter would need to bereplaced more frequently. Bonding the electrostatic filter to the foamfilter ensures that this does not happen. Further, bonding theelectrostatic filter to the foam filter provides a filter core that canbe easily removed from the filter assembly for cleaning. Alternatively,the electrostatic filter may be removably attached to the foam filter.

Preferably, the first filter portion is washable. The first filterportion will generally retain most of the dust or dirt entrained in theairflow. When the filter portion becomes less efficient than is desireddue to excess loading, the user is able merely to wash the filterportion and, after drying, the first filter portion can be returned tothe filter assembly for further use. The maintenance costs of theappliance are thus reduced.

Preferably, the second filter portion is washable. This means that theentire filter assembly can be cleaned by washing, which in turn meansthat replacement filters are not required. When the filter assemblybecomes less efficient than is desirable due to excess loading, the useris able to wash both the first and second filter portions and, afterdrying, the filter assembly can be returned to the vacuum cleaner (orother appliance) for further use. Advantageously, maintenance costs ofthe appliance are thus reduced.

Preferably, the first and second filter portions are at least partiallyenclosed by means of the filter housing. Preferably, at least one of thefilter portions is bonded to the filter housing. More preferably, thesecond filter portion is bonded to the filter housing. This ensures thatthe second filter portion cannot be misplaced or misaligned when thefirst filter portion is removed for washing.

Preferably, the first filter portion has a tab or gripping portionlocated on a surface thereof remote from the second filter portion tofacilitate removal of the first filter portion from the filter housing.Advantageously, this provides a means for removing the first filterportion from the filter housing, when it needs to be cleaned, withoutthe user having to directly handle it.

Further advantageous features are set out in the subsidiary claims.

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1a is a plan view of a first filter assembly according to theinvention;

FIG. 1b is a sectional view taken along line b—b of FIG. 1a;

FIG. 2 is an exploded view of the filter assembly of FIG. 1a;

FIGS. 3a, 3 b and 3 c are plan, side and perspective views respectivelyof a first filter portion forming part of the filter assembly shown inFIGS. 1 and 2;

FIGS. 4a and 4 b are plan and side views respectively of a second filterportion forming part of the filter assembly shown in FIGS. 1 and 2;

FIG. 5 is a sectional view of a second filter assembly according to theinvention;

FIGS. 6a and 6 b are perspective and sectional views respectively of thefilter assembly of FIG. 5 shown on a reduced scale and showing the firstfilter portion in a partially removed position; and

FIG. 7 is an exploded perspective view of a third filter assemblyaccording to the invention and similar to that shown in FIGS. 5, 6 a and6 b.

A first embodiment of a filter assembly according to the presentinvention is shown FIGS. 1a, 1 b and 2. The filter assembly 10essentially comprises a filter housing 12, a first filter portion 14 anda second filter portion 16. The filter housing 12 is cylindrical inshape and is manufactured from a suitable plastics material. The filterhousing 12 has a cylindrical outer wall 18 which is adapted to receivethe first and second filter portions 14, 16. A cylindrical sleeve 20 islocated inwardly of the cylindrical outer wall 18 and is connectedthereto by radially projecting arms or spokes 22 which extend between anend face of the cylindrical sleeve 20 and an end face of the cylindricalouter wall 18. As can be seen from FIG. 2, the spokes 22 lie generallyin the plane of one end of the cylindrical outer wall 18. Thecylindrical outer wall 18, the cylindrical sleeve 20 and the spokes 22are manufactured integrally by means of known plastics formingtechniques.

A central gripping portion 24 is provided on or within the cylindricalsleeve 20. It is also integrally moulded with the cylindrical outer wall18, the cylindrical sleeve 20 and the spokes 22. The central grippingportion 24 essentially comprises a generally cylindrical portion 25 witha plate-like portion 26 extending therefrom along the axis of the filterhousing 12. The plate-like portion 26 provides a user with the means tograsp the central gripping portion 24 in order to insert the filterassembly 10 into the appliance in which it is to be used, or to removeit therefrom. The plate-like portion 26 can incorporate a texturedsurface which will assist the user to grip the connector portion 24. Theplate-like portion 26 is dimensioned so that it projects beyond the endsurface of the filter housing 12 as shown in FIG. 1b. This feature canbe used in conjunction with the vacuum cleaner in order to prevent theuser from inadvertently positioning the filter assembly 10 in therelevant appliance in an incorrect orientation. More specifically, thevacuum cleaner will include a recess or other shaping into which thefilter housing 12 is to be received, but the recess will not include anyaccommodation for the projecting plate-like portion 26. This ensuresthat the user will be unable to seat the filter housing 12 in the recessin the vacuum cleaner if the filter housing 12 is turned the wrong wayup. The user will be alerted to this and will be able to correct theorientation of the filter housing 12.

It will be appreciated that the central sleeve 20 and/or the centralgripping portion 24 can carry means for fixedly connecting the filterassembly 10 to the relevant appliance. The manner in which the filterassembly 10 is connected to the appliance is material to this inventionand a skilled reader will appreciate that the connection can be formedby the mating of camming surfaces, by screw-threaded portions, bysnap-fitting/quick-release fasteners or other equivalent means.

It is essential that the spokes 22 are arranged and configured so that arelatively small proportion of the area of the end face of the filterhousing 12 in which the spokes 22 lie is obstructed by them. In theillustrated embodiment, eight spokes 22 are equi-angularly arrangedabout the cylindrical sleeve 20. However, the number of spokes 22provided is not critical and it is envisaged that fewer or more thaneight spokes 22 can be present. As few as four spokes and as many assixteen spokes are expected to be acceptable, with eight or twelvespokes being preferred.

The first and second filter portions will now be described withreference also to FIGS. 3 and 4. The first filter portion 14 comprises afoam filter 14 a and an electrostatic filter 14 b. A suitable materialfrom which the foam filter 14 a can be manufactured is 90 ppireticulated open cell polyurethane foam. The foam filter 14 a is shapedand configured to form a cylindrical disc having a central aperture 14c. The foam filter 14 a is dimensioned so as to substantially fill theinterior of the filter housing 12. Therefore, the outer diameter of thefoam filter 14 a is substantially the same as the diameter of thecylindrical outer wall 18 of the filter housing 12, and the diameter ofthe central aperture 14 c of the foam filter 14 a is substantially thesame as that of the cylindrical sleeve 20. In order to ensure that theinterior of the filter housing 12 is reliably filled, it is preferredthat the outer diameter of the foam filter 14 a is slightly larger thanthe interior diameter of the cylindrical outer wall 18, and the diameterof the central aperture 14 c of the foam filter 14 a is slightly smallerthan the outer diameter of the cylindrical sleeve 20. The electrostaticfilter 14 b is manufactured from a sheet of suitable electrostaticmedium, for example, Technostat®. The electrostatic filter 14 b iscircular in shape and has a central aperture 14 d. The electrostaticfilter 14 b is dimensioned so that the outer diameter thereof issubstantially the same as the outer diameter of the foam filter 14 a andthe central aperture 14 d of the electrostatic filter 14 b issubstantially the same as the central aperture 14 c of the foam filter14 a. The electrostatic filter 14 b is bonded to the foam filter 14 a bysuitable means so that the central aperture 14 c and the centralaperture 14 d are aligned. Alternatively, the electrostatic filter 14 bcan be placed adjacent the foam filter 14 a without being bondedthereto.

A tab 28 is provided on the first filter portion 14 in order to assistwith the removal of the first filter portion 14 from the filter housing12. The tab 28 can take any suitable form. In the embodiment shown, thetab 28 consists of a flexible elongate strand 28 a having a securing tab28 b at one end and a gripping tab 28 c at the other end. The securingtab 28 b is pushed through the foam filter 14 a and the electrostaticfilter 14 b of the first filter portion 14 in a manner commonly used inrelation to textile materials and goods made therefrom. The strand 28 ais made sufficiently long to ensure that the gripping tab 28 c isaccessible to the user in order to effect the removal of the firstfilter portion 14 from the filter housing 12. Alternatively, a simpletextile or plastics tab could be secured to the outer surface of thefirst filter portion 14 by adhesives or by other means.

The second filter portion 16 is illustrated in FIGS. 4a and 4 b. Thesecond filter portion 16 consists of a HEPA grade filter medium coveredon both sides by layers of a protective fabric. The layers are heldtogether in known manner by stitching or other known means. The secondfilter portion 16 is circular in shape with a central aperture 16 a forreceiving the cylindrical sleeve 20 of the filter housing 12. Thedimensions of the second filter portion 16 are chosen so that the secondfilter portion 16 covers the end face of the filter housing 16 in whichthe spokes 22 are formed. The second filter portion 16 is locateddirectly adjacent the spokes 22 of the filter housing 12 and is bondedto the portion of the cylindrical outer wall 18 immediately adjacent theouter ends of the spokes 22. In this manner, the second filter portion16 is held in a fixed position with respect to the filter housing 12.The second filter portion 16 is bonded to the filter housing 12 by anysuitable method. Suitable methods include heat welding, ultra-sonicwelding and adhesive. It is preferred that, during the bonding process,all of the layers of the second filter portion 16 are bonded to thefilter housing 12 so that the risk of delamination of the second filterportion 16 during washing is reduced.

As can be seen from FIGS. 1 and 2, the assembly is arranged so that thesecond filter portion 16 is located directly adjacent the spokes 22 ofthe filter housing 12 and the first filter portion 14 is then locatedwithin the cylindrical outer wall 18 of the filter housing 12 directlyadjacent the second filter portion 16. The electrostatic filter 14 b ofthe first filter portion 14 lies directly adjacent the second filterportion 16.

In use, the filter assembly 10 is placed in the airflow path of thevacuum cleaner or other appliance in which the filter assembly 10 is tobe used. The plate-like portion 26 is used to ensure that the filterhousing 12 is correctly orientated. Specifically, the filter assembly 10is arranged so that the open face of the filter housing 12, i.e. the endface remote from that in which the spokes 22 are arranged, facesupstream. Air to be filtered therefore enters the foam filter 14 afirst. Filtration takes place within the foam filter 14 a which has avery significant capacity for trapping and retaining dust. However,continued use, particularly within a vacuum cleaner, may lead to anincrease in the back pressure applied to the filter assembly 10. Anydust that may escape the foam filter 14 a is trapped by theelectrostatic filter 14 b of the first filter portion 14. In the eventthat the first filter portion 14 is not removed and cleaned by washingbefore the back pressure applied across the filter assembly 10 reaches acritical value, dust previously retained within the first filter portion14 will be expelled therefrom. However, the presence of the secondfilter portion 16 immediately downstream of the first filter portion 14ensures that any dust released by the first filter portion 14 isretained within the filter assembly 10. When a filter assembly 10 ofthis sort is used as a pre-motor filter in a vacuum cleaner or otherappliance, the motor is thereby reliably protected. Even when the filterassembly 10 is fully loaded with dust, there is still no emission ofpreviously retained dust from the filter assembly 10 and the motorcontinues to be protected. Indeed, in this event, either the backpressure across the filter assembly 10 or the rise in operatingtemperature of the motor will normally be sufficient to operate awarning light to indicate to the user that the filter assembly requiresto be removed and cleaned.

As has been mentioned above, the first filter portion 14 can be cleanedby washing. The second filter portion 16 is also capable of beingcleaned by washing. If the second filter portion 16 is bonded to thefilter housing 12, the second filter portion 16 and the filter housing12 must be washed together. If the second filter portion 16 is notbonded to the filter housing 12, then the second filter portion 16 canof course be washed independently of the filter housing 12. However,care must then be taken to replace the second filter portion 16 in thefilter housing 12 in a position which does not allow any air to passthrough the filter assembly 10 without passing through the second filterportion 16.

It will be appreciated that the filter assembly described above can bemanufactured with any appropriate dimensions. Purely for the purposes ofillustration and without any intent to limit the disclosure herein, thedimensions of the filter housing 12 illustrated above are in the regionof 140 mm diameter and 25 mm depth.

A second embodiment of a filter assembly according to the invention isillustrated in FIGS. 5, 6 a and 6 b. As can be seen from the Figures,the filter assembly 100 is again generally cylindrical in shape. Incontrast to the embodiment illustrated in FIGS. 1 to 4, the axial lengthof the filter assembly 100 is greater than the diameter thereof.

The filter assembly 100 comprises a first housing portion 102 and asecond housing portion 104. The first housing portion 102 is generallycircular in shape and has a planar central portion 106 which issurrounded by a circular dished portion 108. Two outwardly projectinglocating legs 110 are equispaced about the dished portion 108 and theseextend away from the base of the dished portion 108 as shown in theFigures. The second housing portion 104 is annular in shape having anaperture in the centre thereof and a side wall 112 which mirrors theoutermost extremity of the dished portion 108 of the first housingportion 102. An annular lip 114 extends radially outwardly from thedistal edge of the side wall 112.

A HEPA grade filter 116 is located between the first and second housingportions 102, 104. The HEPA grade filter 116 comprises a pleat pack of102 pleats of washable HEPA grade filter material which is arranged in acylindrical form. A first end 116 a is seated in the dished portion 108of the first housing portion 102 and is bonded thereto by suitablemeans. Suitable means include potting, adhesives, etc. The bonding ofthe first end 116 a of the HEPA grade filter 116 into the dished portion108 is of sufficient quality to prevent any passage of air around theend of the HEPA grade filter 116 within the dished portion 108. Theother end 116 b of the HEPA grade filter 116 is seated in the secondhousing portion 104 radially inwardly of the side wall 112. The end 116b of the HEPA grade filter 116 is bonded to the second housing portion104 by potting or adhesives or other suitable means. In this manner, thefilter assembly 100 is given a cylindrical structure comprising thefirst and second housing portions 102, 104 and the HEPA grade filter116.

A filter core 150 is provided radially inwardly of the HEPA grade filter116. The filter core 150 comprises a cylindrical foam filter 120 and anelectrostatic filter 121 located on the radially outer surface of thefoam filter 120. The electrostatic filter 121 can be bonded to thecylindrical foam filter 120 by suitable means. Alternatively, theelectrostatic filter 121 can be slipped over the cylindrical foam filter120 without being bonded thereto. The filter core 150 is closed at alower end by a circular disc portion 152. The disc portion 152 issecurely bonded to the lower end by potting, adhesives, etc. The outerdiameter of the filter core 150 is essentially the same as the internaldiameter of the HEPA grade filter 116. This ensures that, when thefilter core 150 is located inside the HEPA grade filter 116, the filtercore 150, particularly the electrostatic filter 121, abuts against theinternal surface of the HEPA grade filter 116. The internal diameter ofthe filter core 150 is sufficiently large to allow unrestricted entry ofa dust-laden airflow into the interior of the filter assembly 100.

As shown in FIGS. 6a and 6 b, a first end 120 a of the filter core 150has a gripping portion 122 attached thereto. The gripping portion 122 ispreferably formed from potting so as to provided a resilientlydeformable gripping portion which is securely bonded to the end 120 a ofthe filter core 150. Alternatively, the gripping portion 122 could bemoulded from a plastics material and bonded to the filter core 150 by asuitable adhesive. The gripping portion 122 is dimensioned and shaped sothat its outermost extremity 124 abuts against the periphery of theaperture in the second housing portion 104 in a sealing manner when thefilter core 150 is inserted into the filter assembly 100. The axiallength of the filter core 150 is such that, when the outermost extremity124 of the gripping portion 122 is in sealing contact with the secondhousing portion 104, the disc portion 152 of the filter core 150 pressesagainst the central portion 106 of the first housing portion 102. Thegripping portion 122 is annular in shape and has a central aperturecommunicating with the interior of the filter core 150.

A third embodiment of the filter assembly is shown in FIG. 7. The filterassembly 100′ has substantially the same construction as the filterassembly 100 shown in FIGS. 5, 6 a and 6 b, with the exception that theend 116 b′ of the HEPA grade filter 116′ is sealed and the filterassembly 100′ includes an outer casing 156. The end 116 b′ is sealed bysuitable means, for example, potting, adhesives, etc. The end 116 b′abuts against the interior surface of the second housing portion 104′.The outermost extremity 124′ of the gripping portion 122′ is securelybonded to the second housing portion 104′. The casing 156 is cylindricalin shape and is manufactured from a suitable plastics material. Thecasing 156 is adapted to receive the HEPA grade filter 116′. An end 158of the casing 156 is seated in the dished portion 108′ and is bondedthereto by suitable means, for example, adhesives or potting. Slots 160are provided in the casing 156 to allow air to diffuse out of the filterassembly 100′. The casing 156 provides protection for the HEPA gradefilter 116′ during handling.

The airflow path through the filter assemblies 100, 100′ issubstantially the same for either embodiment. The description belowrefers to the second embodiment but it will be appreciated that thedescription equally applies to the third embodiment. In use, the filterassembly 100 is placed upstream of the motor and fan assembly of avacuum cleaner. The airflow path of the vacuum cleaner is designed andarranged so that air exiting the main dirt and dust collectingapparatus, preferably a cyclonic separating apparatus, enters the filterassembly 100 by way of the aperture in the gripping portion 122. The airthen passes into the cylindrical passage surrounded and delimited by thefilter core 150. The end of this passage remote from the grippingportion 122 is closed by the disc portion 152 and the central portion106 of the first housing portion 102. Because the filter core 150presses against the central portion 106, the only available exit fromthe passage is through the cylindrical foam filter 120. The airtherefore moves radially outwardly away from the longitudinal axis 126of the filter assembly 100. Having passed through the cylindrical foamfilter 120, the airflow continues radially outwardly in the direction ofthe arrow 128 and passes through the electrostatic grade filter 121. Theairflow then passes through the HEPA grade filter medium of the secondfilter portion 116 before exiting the filter assembly 100 in a radialdirection.

Under normal operational circumstances, the vast majority of any finedust entrained within the airflow entering the filter assembly 100,100′will be trapped within the pores of the cylindrical foam filter 120 andthe electrostatic filter 121. Little or no dust will be collected in theHEPA grade filter 116. This is because the cylindrical foam filter 120has a large capacity for retaining dust particles and any dust that mayescape from the cylindrical foam filter 120 will be trapped by theelectrostatic filter 121 of the filter core 150. When the filter core150 is approaching its loading capacity, it should ideally be removedand cleaned. This can be achieved merely by the user gripping thegripping portion 122,122′ and lifting the filter core 150 out of thefilter assembly 100 in the direction of arrow 130 as shown in FIGS. 6aand 7. The filter core 150 is then washed by rinsing under a householdtap in a known manner and allowed to dry. The filter core 150 is thenre-inserted into the interior of the filter assembly 100,100′ andoperation can continue.

It is preferred that the HEPA grade filter material from which the HEPAgrade filter 116 is made should be washable. This ensures that the HEPAgrade filter 116 does not degrade or deteriorate to any significantextent in the event that the filter core 150 is returned to use beforeit is completely dry. Also, it is possible that the filter core 150 willnot be cleaned by washing before its loading capacity is exceeded. Inthis event, dust previously trapped by the filter core 150 maybeexpelled therefrom. Any and all dust expelled from the filter core 150will inevitably be trapped and captured by the HEPA grade filter 116. Ifa significant amount of dust is allowed to accumulate on the HEPA gradefilter 116, it can then be washed by rinsing under a household tap andallowed to dry. Operation of the vacuum cleaner can then be resumed.

The locating legs 110 are illustrated in FIGS. 5, 6 b and 7 as beingequispaced about the longitudinal axis 126 of the filter assembly100,100′. If the vacuum cleaner or other apparatus in which the filterassembly 100,100′ requires a specific rotational orientation of thefilter assembly 100,100′, then an asymmetrical arrangement of locatinglegs can be provided so that the filter assembly 100,100′ cannot beproperly located in the appliance in any orientation other than thecorrect one. However, with airflow entry being arranged axially andairflow exit being allowed in all rotational directions as illustratedin FIGS. 5, 6 a, 6 b and 7, this is not necessary.

Modifications and variations will be apparent to a skilled reader. Meansand devices for holding the filter assembly in the relevant applianceand for correctly orientating it in position, other than those mentionedabove, are not intended to be excluded from protection. It will also beappreciated that the shape of the filter or filter housing need not becylindrical and other shapes will be equally suitable. Indeed, thefilter housing shown in FIGS. 1 to 4 need not be open on one side whenthe filter assembly is in use: the filter housing could take the form ofa cage-like structure having closed side walls but with both endsurfaces defined by spokes or a mesh. One or both end surfaces could beremovable or openable to allow access to the filter portions forcleaning purposes. Either or both of the cylindrical sleeve and thecentral gripping portion may be omitted from the filter housing. If thecentral sleeve is omitted, the central apertures of the first and secondfilter portions will also be omitted. Other variations will be apparentto a skilled reader.

What is claimed is:
 1. A filter assembly configured and sized for use ina vacuum cleaner, comprising a filter housing, a first filter portioncomprising a foam filter and an electrostatic filter bonded to the foamfilter, and a second filter portion located downstream of the firstfilter portion and comprising a HEPA grade filter medium, the first andsecond filter portions being held directly adjacent one another withinthe filter housing, the foam filter of the first filter portion beingconfigured so that, in use, the foam filter is exposed directly to adust-laden airflow, and the first filter portion being configured so asto be removable from the filter assembly, wherein the electrostaticfilter is located on the side of the foam filter facing the secondfilter portion.
 2. A filter assembly as claimed in claim 1, wherein thefirst filter portion is washable.
 3. A filter assembly as claimed inclaim 1, wherein the second filter portion is washable.
 4. A filterassembly as claimed in claim 1, wherein the filter housing is formedfrom a plastic material.
 5. A filter assembly as claimed in claim 1,wherein at least one of the filter portions is bonded to the filterhousing.
 6. A filter assembly as claimed in claim 5, wherein the secondfilter portion is bonded to the filter housing.
 7. A filter assembly asclaimed in claim 1, wherein the filter housing has an open side adaptedto allow introduction of the first filter portion into the interior ofthe filter housing.
 8. A filter assembly as claimed in claim 1, whereinthe first filter portion has a tab or gripping portion located on asurface thereof remote from the second filter portion to facilitateremoval of the first filter portion from the filter housing.
 9. A filterassembly as claimed in claim 1, wherein the first filter portion iscylindrical in shape and is closed at one end.
 10. A filter assembly asclaimed in claim 1, wherein the filter housing further compriseslocating means for preventing incorrect orientation of the filterhousing within the vacuum cleaner.
 11. A filter assembly as claimed inclaim 10, wherein the locating means comprises a projection located onthe filter housing and extending outwardly therefrom.
 12. A filterassembly as claimed in claim 1, wherein the filter assembly is generallycylindrical in shape.
 13. A filter assembly as claimed in claim 12,wherein the filter assembly is configured so that, in use, the directionof flow of the airflow sequentially through the first and second filterportions is generally parallel to a longitudinal axis of the cylindricalfilter assembly.
 14. A filter assembly as claimed in claim 13, wherein,in use, the direction of the flow of the airflow sequentially throughthe first and second filter portions is generally radial relative to thelongitudinal axis of the filter assembly.
 15. A vacuum cleaner having anairflow path and comprising at least one filter assembly as claimed inclaim 1 located in the airflow path.
 16. A vacuum cleaner as claimed inclaim 15, further comprising a motor for causing air to flow along theairflow path, wherein the filter assembly is positioned upstream of themotor.